MONDAY, July 18 (HealthDay News) -- Researchers on Monday released yet more evidence that early treatment of HIV in an infected heterosexual can protect his or her partner from becoming infected.

The study, conducted among 1,763 couples in Africa, Asia, South America and the United States, found that HIV-infected people in stable sexual relationships cut their odds of transmitting the virus to their partner by 96 percent if they got antiretroviral medications soon after diagnosis.

The findings were published online ahead of print in the New England Journal of Medicine to coincide with their presentation on Monday at the International AIDS Society Conference in Rome.

To the question of whether early treatment helps shield sexual partners from infection, the answer from this study "was a resounding yes," Dr. Scott Hammer, professor of medicine at Columbia University, New York City, wrote in an accompanying journal editorial.

The new findings come on the heels of similar research released July 13 by the U.S. Centers for Disease Control and Prevention. In two separate studies, scientists found that giving antiretroviral drugs to heterosexuals at high risk of HIV infection significantly reduced their chances of developing the AIDS-causing virus.

Speaking to HealthDay at the time, Dr. Jared Baeten, co-chair of one study and a University of Washington associate professor of global health, called that outcome "an extremely exciting finding for the field of HIV prevention."

In the latest study in NEJM, a team led by Dr. Myron S. Cohen at the University of North Carolina at Chapel Hill tracked outcomes for couples where one partner was HIV-positive and the other was not (evenly split between males and females carrying the virus). The infected partner was randomized to receive a combination of a variety of standard HIV-suppressing medications, either immediately after their diagnosis or in a delayed fashion (for example, until their immune cell counts reached a certain low level, or when HIV-linked symptoms appeared).

Enrollment in the trial began in June of 2007 and by the end of February 2011 the team used gene-based methods to confirm 28 cases where a previously uninfected partner had contracted the virus from his or her HIV-positive mate.

In only one of the 28 cases, the transmission had occurred in a couple randomized to the early-treatment group.

"The sustained suppression of HIV-1 in genital secretions resulting from antiretroviral therapy is the most likely mechanism for the prevention of HIV-1 transmission that we observed," Cohen's team wrote.

They also found early treatment to be associated with a 41 percent drop in HIV-linked "clinical events" -- sickness and/or death -- in HIV-infected patients, compared with those whose treatment was delayed.

The findings echo those reported by the CDC last week. Both of the CDC trials were done in Africa. In one, a daily dose of Truvada, a combination pill that includes tenofovir disoproxil fumarate and emtricitabine, reduced the risk of contracting HIV from infected partners by about 63 percent.

The other study found that two different regimens -- tenofovir, sold as Viread, and Truvada -- also reduced the risk of transmission through heterosexual sex.

No significant safety concerns were associated with Truvada, the study said, although people taking it were more likely to report nausea, vomiting and dizziness than those taking placebo.

Using antiretrovirals in this way is called pre-exposure prophylaxis, or PrEP.

Earlier research has found that PrEP reduced HIV transmission among gay and bisexual men, but whether it could prevent HIV infection among heterosexuals had remained unknown.

"Now, more than ever, the priority for HIV prevention research must be on how to deliver successful prevention strategies, like PrEP, to populations in greatest need," Baeten said last Wednesday.

Based on the recent findings, the CDC will start working to develop guidance on the use of PrEP among heterosexuals in the United States, the agency said.

"To use PrEP in the United States we would use basically the same guidelines -- someone who is truly at risk for HIV," said Dr. Margaret A. Fischl, professor of medicine and director of the AIDS Clinical Research Unit and co-director of the University of Miami Developmental Center for AIDS Research, commenting on the studies released July 13.

Those at high-risk have multiple sex partners, use intravenous drugs or have multiple sexually transmitted diseases, Fischl said. "You are talking about a group that is at risk for multiple sexually transmitted diseases including HIV," she said.

However, it might be difficult to get the drugs to the people who need them, Fischl added.

"In addition, we need to identify people with HIV and get them into care, because in doing that we know that we decrease the transmission of HIV," Fischl said.